Hydroxypropyl Cyclodextrins, chemical derivatives of glucose oligosaccharides, which were originated in the section, form water soluble complexes with lipophiles. Since these derivatives are also non-toxic they have been used as drug solubilizers with enough of success to qualify them for consideration to be included in the next edition of US Pharmacopea/National Formulary. Since hydroxypropyl cyclodextrins are amorphous mixtures of chemical individua and thus difficult to characterize, the present work of the section has been focused on the effects which preparative conditions may have on their properties. The reactivity of cyclodextrins was investigated, the mixtures subjected to a detailed analysis, several components of these and of similar mixtures were isolated as chemical individua, crystallized and their crystal structure determined.